I have just got to grips with making an index I think. I appreciate this is is work in progress, but I feel a small change might make a lot of difference. At the moment you have to make the index entries visible by enabling Field Shadings, then select an entry, the right click on it to see the edit dialogue.
Suppose the edit dialogue could be bought up from wherever the cursor currently is by right-clicking. There would be no current index entry, but you could still go to the next one or the previous one using the buttons (so making them visible is not as important - make them visible when the dialogue is up). You could create an index entry from this menu, just like the other dialogue (the button is there, and you would not have a current entry to overwrite of the cursor was not on an index entry). You would not have to close this dialogue to create a new entry - just move the cursor.